As a type of door closer, a floor hinge embedded in a floor is disclosed in Patent Literature 1. The floor hinge proposed by the present applicant in Patent Literature 1 is configured to include a spring retaining seat on a fixed side, a return spring, and a piston in this order from the side closest to a main shaft. In other words, the floor hinge is configured such that the return spring is interposed between the piston and the spring retaining seat on the fixed side and an end surface of the piston on the main shaft side serves as a spring retaining seat on a moving side. The piston moves toward the spring retaining seat on the fixed side when a door is opened, and accordingly, the return spring is compressed to store the closing force. The floor hinge is configured to use the closing force (spring force) of the return spring to rotate the main shaft and automatically close the door.